|Publication number||US7348087 B2|
|Application number||US 10/628,946|
|Publication date||Mar 25, 2008|
|Filing date||Jul 28, 2003|
|Priority date||Jul 28, 2003|
|Also published as||US7981560, US20050026016, US20100279207|
|Publication number||10628946, 628946, US 7348087 B2, US 7348087B2, US-B2-7348087, US7348087 B2, US7348087B2|
|Inventors||Daniel A Kearl, David Champion, Gregory S Herman, Richard B. Peterson|
|Original Assignee||Hewlett-Packard Development Company, L.P.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (19), Non-Patent Citations (8), Classifications (15), Legal Events (6)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This invention relates to fuel cells and more particularly to a MEMS-based planar fuel cell having an integral manifold and to methods for making and using such fuel cells.
Various portable devices, such as laptop computers, personal digital assistants (PDA's), portable digital and video cameras, portable music players, portable electronic games, and cellular phones or other wireless devices, require portable power sources. The weight and inconveniences of single-use batteries and rechargeable batteries have motivated efforts to replace those power sources for portable use. Thus, there is an increasing demand for light-weight, re-usable, efficient, and reliable power sources in such applications and in many other applications as well. In attempts to meet these needs, various portable fuel cells have been developed, such as ceramic-based solid-oxide fuel cells, direct methanol fuel-cell (DMFC) systems, reformed-methanol-to-hydrogen fuel-cell (RMHFC) systems, and other proton-exchange-membrane (PEM) fuel-cell systems. Microscale design principles have been applied to the design of portable fuel cells to provide improved power density and efficiency and to provide lower cost. However, microscale fuel-cell designs can be difficult to supply with fuel and oxidant in ways that do not interfere with the purposes of the microscale design. Similarly, it can also be difficult to exhaust depleted fuel and oxidant in a microscale-compatible manner. Although nanoscale manifolding with minimum dimensions below one micrometer has been developed for sensors and other purposes, the scale of such nanoscale manifolding is ill-suited for microscale fuel cell designs. There is a continuing need and a large anticipated market for improved practical compact portable fuel cells with rapid startup times and improved efficiency. There is a particular need for compact portable fuel cells with improved microscale manifolding of supplied fuel and/or supplied oxidant and with improved microscale manifolding for exhausting depleted oxidant and/or depleted fuel from the fuel-cell active region.
The features and advantages of the disclosure will readily be appreciated by persons skilled in the art from the following detailed description when read in conjunction with the drawings, wherein:
Throughout this specification and the appended claims, the term “fuel cell” means a fuel cell in its usual meaning or a battery cell having at least one each of an anode, a cathode, and an electrolyte. A “unit cell” is one cell comprising an anode, a cathode, and an electrolyte. The term “MEMS” has its conventional meaning of a micro-electro-mechanical system. The prefix “micro-” and the term “microscale” refer to structures having minimum dimensions of the order of about one micrometer. The verb “flowing” is used in a transitive sense, meaning causing a flow of a fluid. The term “lateral” is used to mean generally parallel to the principal plane of a generally planar unit cell. For clarity of the description, the drawings are not drawn to a uniform scale. In particular, vertical and horizontal scales may differ from each other and may vary from one drawing to another.
In accordance with one aspect of the invention, a MEMS-based fuel cell 10 has a substrate 20, an electrolyte 30 in contact with the substrate, a cathode 40 in contact with the electrolyte, an anode 50 spaced apart from the cathode and in contact with the electrolyte, and an integral manifold 60 for supplying either a fuel or an oxidant or both together. The integral manifold 60 extends over at least a portion of the electrolyte 30 and over at least one of the anode 50 and/or cathode 40. In some embodiments of such a fuel cell, electrolyte 30 is also the substrate 20, as will be made clear hereinbelow. Such a fuel cell may also be a unit cell in a fuel-cell assembly comprising a number of unit cells with suitable electrical connections. The unit cells may be stacked to form the fuel-cell assembly, for example, or may be arranged in a planar array.
Also shown in
Similarly, by reversing the designations of anode and cathode in
Also shown in
The fuel cell may include a conventional current collector, e.g., a patterned film of conductive material (not shown) and at least a portion of the current collector may be disposed on an exterior surface of the integral manifold 60 or adjacent to an exterior surface of the integral manifold 60. In some embodiments, the current collector may be disposed on the roof of manifold 60.
Thus, another aspect of the invention provides a manifold 60 for a fuel cell, the manifold itself having a substrate and an elongated roof affixed to the substrate. Generally, the roof may be semi-cylindrical or have a rectangular or trapezoidal cross-section, for example. The roof encloses an elongated interior volume communicating with the electrolyte and with at least one of the anode and cathode of the fuel cell. The interior volume generally may be semi-cylindrical, rectangular, or trapezoidal, for example. As described hereinabove, the manifold 60 may have an opening 80 or 90 extending through the substrate, whereby the interior volume of the manifold further communicates with the opening through the substrate.
As shown in
The various forms of manifold 60 provide integral means for supplying the fuel and/or the oxidant, and/or for exhausting depleted fuel and/or depleted oxidant. To do so, the various forms of manifold 60 extend over at least a portion of the electrolyte and over at least a portion of the anode and/or cathode. Those skilled in the art will recognize that fuel and oxidant inputs are conventionally provided from external sources and that exhausts of any depleted fuel and any depleted oxidant are conventionally directed to external outputs.
In accordance with another aspect of the invention, a MEMS-based fuel cell 10 using a fuel and an oxidant may be fabricated by an overall method described below with reference to
The overall fabrication method, shown in
Those skilled in the art will recognize that the order of cathode and anode depositions and subsequent sintering may be inverted, depending on processing temperature requirements, for example. The chamber 70 includes at least one integral manifold 60 for the fuel and/or oxidant. The chamber may extend over at least the entire anode, for example. Other steps are described hereinbelow in connection with more specific methods.
For some embodiments, a portion of the substrate the anode and cathode of the unit cell may be removed (step S60), e.g., by conventional wet etching or dry plasma etching, leaving a supporting membrane portion. Also, for some embodiments, the method includes a step of patterning the electrolyte. The electrolyte-depositing step may comprise depositing a solid-oxide electrolyte or a proton-exchange-membrane (PEM) electrolyte, for example.
Various methods for forming chamber 70 are illustrated in
Sacrificial material 55 may be silicon (polycrystalline or amorphous), oxides of silicon, spin-on-glass (SOG) compounds, photoresists, pyrolyzable polymers, and other release films conventionally used in the field of MEMS fabrication. A selection criterion for these sacrificial films is their etch selectivity in comparison with the other fuel-cell materials used in the structure. A suitable sacrificial polymer material is a polynorbornene, such as Unity™ Sacrificial Polymer, which may be cleanly removed by pyrolysis at 350-425 C. This material is commercially available from Promerus Electronic Materials of Brecksville, Ohio. Alternative polymers for some applications are polymethylmethacrylate (PMMA), polystyrene, or polyparaxylene (Parylene™) and derivatives of the latter polymer, for example.
Some suitable materials to form the chamber roof for various embodiments are silicon oxide, silicon nitride, silicon oxynitride, silicon carbide, aluminum oxide, spin-on-glass (SOG) compounds, polyimides (e.g., for low temperature cells), other photopolymer systems, and the actual fuel cell electrolyte material itself. A suitable photopolymer for some embodiments is a negative, epoxy-type, near-UV photoresist based on EPON™ (e.g., SU-8, available from MicroChem Inc. of Newton, Mass.). Thus, a suitable material to form the chamber roof may be an electrolyte or a non-electrolyte.
As described hereinabove, manifold 60 may include a porous substance 120 substantially filling the interior volume of the manifold. Porous substance 120 may serve as an electrode. The method for forming chamber 70 illustrated in
Another method for forming chamber 70 is illustrated in
As shown in
Manifold 60 of chamber 70 may be formed by tape-casting the electrolyte 30. A method for forming manifold 60 of chamber 70 is illustrated by
In preparing the unfired tape 35 of electrolyte material carrying the cathode and anode, a cathode material may be deposited and optionally patterned on at least one side of an unfired tape of electrolyte material. Deposition of the cathode material may be done by printing, e.g., by silk-screen-printing. Alternative printing techniques include, but are not limited to transfer printing, spraying through a stencil mask, extrusion printing, extrusion printing with subsequent embossing, and other suitable printing techniques that may occur to those skilled in the art.
In the embodiment of
One or more openings 80 and/or 90 communicating with chamber 70 may be formed through the substrate under the chamber. Openings 80 and/or 90 may be adapted for flow of the fuel and/or oxidant into the chamber or for exhaust flow of depleted fuel and/or depleted oxidant out of the chamber. Similarly, a third opening (not shown) may be formed through the substrate under the chamber, communicating with the chamber and adapted for exhaust flow of depleted fuel and/or depleted oxidant out of the chamber.
By combining various elements of fabrication methods performed in accordance with the invention, a method may be practiced comprising the steps of providing a substrate, depositing (and optionally patterning) an electrolyte upon the substrate, depositing and patterning a cathode in contact with the electrolyte, depositing and patterning an anode spaced apart from the cathode and in contact with the electrolyte, forming a first chamber extending over at least the anode (the first chamber including an integral manifold for the fuel), forming a second chamber extending over at least the cathode (this chamber including an integral manifold for the oxidant), removing at least a portion of the substrate under the anode and cathode (leaving a membrane portion), forming a first opening through the substrate under the first chamber (this opening communicating with the first chamber and being adapted for flow of fuel into the first chamber), and forming a second opening through the substrate under the second chamber (communicating with the second chamber and being adapted for flow of oxidant into that chamber). The membrane portion may be supported around its entire periphery, or at least part of the membrane portion may be removed so as to leave the membrane portion cantilevered.
According to another aspect of the invention, a method is provided for using a manifold in a MEMS-based fuel cell of the type using a fuel and an oxidant. In this method a substrate carrying an electrolyte, a cathode in contact with the electrolyte, and an anode spaced apart from the cathode and in contact with the electrolyte are provided. An integral manifold for at least one of the fuel and oxidant is also provided, the integral manifold extending over at least a portion of the electrolyte and over at least a portion of one of the anode and cathode. At least one of the fuel and oxidant is supplied through the integral manifold to the electrolyte and to at least one of the anode and cathode. An opening extending through the substrate and communicating with the integral manifold may be used for flowing at least one of the fuel and oxidant through the opening and into the integral manifold. Similarly, an opening extending through the substrate and communicating with the integral manifold may be used for flowing at least one of the depleted fuel and oxidant out of the integral manifold and through the opening. A catalytic combustor may be provided within the integral manifold.
Fuel-cell structures made in accordance with the present invention and specially-adapted methods performed in accordance with the invention are useful in manufacture of compact portable fuel cells.
Although the foregoing has been a description and illustration of specific embodiments of the invention, various modifications and changes thereto can be made by persons skilled in the art without departing from the scope and spirit of the invention as defined by the following claims. For example, the order of performing various steps may be varied and various functionally equivalent materials may be substituted for those used in the embodiments described herein.
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|U.S. Classification||429/535, 427/115, 429/495|
|International Classification||H01M8/02, H01M8/10, B05D5/12|
|Cooperative Classification||H01M8/2483, H01M8/241, H01M8/2418, H01M8/0263, H01M8/1004, H01M8/1097, H01M8/0258|
|European Classification||H01M8/10S, H01M8/10B2|
|Dec 9, 2003||AS||Assignment|
Owner name: HEWLETT-PACKARD DEVELOPMENT COMPANY, L.P., TEXAS
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:KEARL, DANIEL A.;CHAMPION, DAVID;HERMAN, GREGORY S.;AND OTHERS;REEL/FRAME:014184/0661;SIGNING DATES FROM 20031117 TO 20031118
|Apr 14, 2009||CC||Certificate of correction|
|Jun 16, 2011||AS||Assignment|
Owner name: EVEREADY BATTERY COMPANY, INC., MISSOURI
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:HEWLETT-PACKARD DEVELOPMENT COMPANY, L.P.;HEWLETT-PACKARD COMPANY;REEL/FRAME:026463/0542
Effective date: 20101029
|Sep 23, 2011||FPAY||Fee payment|
Year of fee payment: 4
|Jan 24, 2014||AS||Assignment|
Owner name: INTELLIGENT ENERGY LIMITED, UNITED KINGDOM
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:EVEREADY BATTERY COMPANY, INC.;REEL/FRAME:032124/0514
Effective date: 20131219
|Sep 4, 2015||FPAY||Fee payment|
Year of fee payment: 8